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Description/Abstract

We present a geotechnical stability analysis for the planar failure of riverbanks, whichincorporates the effects of root reinforcement and surcharge for mature stands of woodyriparian vegetation. The analysis relies on a new method of representing the root distributionin the soil, which evaluates the effects of the vegetation’s position on the bank.The model is used in a series of sensitivity analyses performed for a wide range of bankmorphological (bank slope and height) and sedimentological (bank cohesion and frictionangle) conditions, enabling discrimination of the types of bank environment for whichvegetation has an effect on bank stability. The results indicate that woody vegetationelements have a maximal impact on bank stability when they are located at the ends ofthe incipient failure plane (i.e. at the bank toe or at the intersection of the failure planewith the floodplain) and that vegetation has a greater effect on net bank stability whenit is growing on low, shallow, banks comprised of weakly cohesive sediments. However,the magnitude of these effects is limited, with vegetation typically inducing changes (relativeto non-vegetated banks) in simulated factors of safety of less than 5%. If correct, thissuggests that the well documented effects of vegetation on channel morphology mustbe related to alternative process mechanisms (such as the interaction of vegetation withriver flows) rather than the mechanical effects of vegetation on bank failure, except inspecial cases where the equivalent non-vegetated bank has a highly marginal stability status.